Analysis

Senate Foreign Relations Committee Chairman Bob Corker, a Republican and occasional critic of Trump who is not seeking re-election in 2018, indicated in his November 14 opening remarks that the timing of the hearing was "not specific to anybody".

However, the ranking Democratic member of the committee, Senator Ben Cardin, cited Trump's oft-quoted "fire and fury" remarks aimed at Pyongyang and suggested that the White House was mulling nuclear options (see NORTH KOREA/US: Trump talk increases nuclear risks - September 8, 2017).

While the president's remarks are probably a more bellicose iteration of long-standing US security commitments to use all tools available in defence of allies, concerns about stable decision-making in the Trump administration are prevalent (see PROSPECTS 2018: US foreign policy - November 10, 2017).

No attack restrictions

It only takes 60 seconds from US Strategic Command receiving a verified attack order from the president before US Minuteman-III intercontinental ballistic missiles (ICBMs) are launched.

In contrast to strategic bombers, which can be recalled while in flight, and the 30-60 minutes needed for nuclear-armed submarines to surface and confirm the presidential attack order, the ICBM leg of the US nuclear triad is designed foremost to threaten an adversary credibility with rapid and irreversible retaliation, so as to dissuade adversaried from launching a first strike.

US defence officials and military officers have stated unequivocally that they would refuse to follow an 'illegal' presidential order to launch a nuclear attack.

This response was likely intended to address hinted legislative concerns about Trump's -- or any president's -- suitability to handle decisions involving ambiguity, limited response time and the psychological pressures of a crisis without suggesting that the US military also shared that interpretation.

However, this assertion is uncharted legal territory and verges on the meaningless, given the already extraordinary circumstance of the president ordering a nuclear attack compounded with the military refusing to follow the directions of the constitutional commander-in-chief.

At the November 14 Senate Foreign Relations hearing, the former commander of US Strategic Command, General C. Robert Kehler, stated (in a personal capacity) that the US military would use nuclear weapons, like conventional weapons, in line with the international legal restrictions of the law of armed conflict.

This includes an obligation to not target civilians directly or intentionally. US forces must also adhere to the principle of proportionality, weighing the relative military advantage of a strike to be beyond the relative level of collateral damage. The use of nuclear weapons would in many cases involve mass civilian casualties, let alone secondary deaths from radiation, fire and environmental damage.

However, the task of adhering to the proportionality standard amid the ambiguities of combat is difficult for field commanders in practice, even in lower-level engagements such as airstrikes (see INTERNATIONAL:Debate grows on 'proportionality' in war - March 6, 2009).

It is highly unlikely that the legal considerations cited here would dissuade the president from ordering an attack, or the military from carrying it out. To the contrary, current US Strategic Command Commander John Hyten has suggested that after informing the president an attack order is illegal, the military's second step would be to provide the president with similar (legal) options, including nuclear ones, to achieve their objectives.

Congressional considerations

Given the lack of substantive legal or procedural obstacles to the president ordering an attack, some legislators have sought to add some limits to presidential authority.

Democrats, led by Massachusetts Senator Ed Markey, have drafted a proposal that would require the president to receive a congressional declaration of war before being able to authorise a nuclear first strike, while leaving intact the president's ability to order a retaliatory strike.

While Markey has long championed positions of greater US restraint on nuclear matters, including opposing the US civilian nuclear agreement with India on legal grounds, this measure has no Republican support and appears primarily anti-Trump political symbolism rather than a proposal likely to be revived under a future Democratic administration.

Some Republican members of the Senate Foreign Relations Committee have pushed back against congressional scrutiny of US command-and-control, with one senator suggesting that US adversaries, such as North Korea, would analyse US policymaker remarks for strategic insight.

International comparisons

A country's geopolitical situation and the technical limitations of its nuclear arsenal (size, vulnerability and technological sophistication) play a central role in the arrangements of nuclear command authority.

For example, Pakistan, which worries about a decapitating conventional strike from India destroying its arsenal, may have resolved to delegate nuclear attack authority from the country's civil-military leadership under the prime minister to field commanders in the event of a crisis.

This 'fail-deadly' approach reflects Pakistan's sense of vulnerability to an attack and the centrality of nuclear weapons to its national security (see PAKISTAN: Concern over nuclear programme will grow - November 15, 2017).

In contrast, countries such as China and India have substantial conventional military means to safeguard their national security, are too large to be overrun quickly by an adversary and have more restrictions on their nuclear arsenals.

Chinese and Indian nuclear doctrines, in contrast to those of Russia and the United States, include 'no first use' pledges, meaning they will only use nuclear weapons in response to a nuclear attack, not even a conventional threat to their homelands (see UNITED STATES: Nuclear shift would lack credibility - August 10, 2016). They also have well-institutionalised command-and-control structures in place.

As the world's preeminent military power with a vast network of alliances and facing multiple near-peer and regional competitors, the United States depends on the ability to threaten nuclear attack (however implicitly) to ward off conventional attacks on security partners in the Baltics, South Korea and Japan (see US/INT: Trump policies will increase nuclear tensions - September 22, 2017).